At a simplistic level, the reason why we don't see more diversity in comics characters is because there's little diversity in comics creators. A lot of privileged white folks are making comics, and so they follow the old "write what you know" saw and fill their stories with white people like themselves. But here's an easy way to shake things up.
MapCrunch.com. It taps into Google's street view and pulls up shot of a random location. That's where your new character and/or their ancestors are from. Maybe not that exact spot (I just called up the middle of a forest in Poland) but that general area. Sure, sometimes, you're going to get a nice neighborhood in New England where all the rich, white folks live but you're sometimes going to get a slum in Thailand. Or a military base in Singapore. Or a small village in Hungary. Or a few houses overlooking a fjord in Norway. (All of which are locations I just randomly called up using MapCrunch.)
Bam. Instant diversity. You've immediately given this new character texture and background completely separate and unique from the rest of your cast without having to do anything more than click a link.
"But what if I need this character to be a certain type of character?"
Why does that matter? I mean, why does your character need to be from a certain location? If you just need to show your character's boss, why couldn't she or he be from Spain? If you need to introduce a love interest, what's wrong with their coming from Iceland? That new antagonist to spur your hero onto greatness can be from Estonia just as readily as Chile.
Plus, I'm not suggesting that these characters need to have just stepped off the metaphoric boat either. Maybe it was their parents or grandparents who emigrated to wherever your story takes place. Like I said, I'm just talking about texture and background here.
Now, sure, you could easily come up with some country you know nothing about. But how difficult is it to look that up on Wikipedia anymore? I'm not suggesting your new character needs to start spouting off the GDP and principle exports of Andorra, so you don't need to become an expert. Again, I'm just talking texture and background.
So with with a single click for each new character, you can broaden your comic's scope and diversity. It will instantly seem more inclusionary than everybody else's because their characters all look and act the same. And you didn't even have to rack your brain trying to figure out what nationality or race would make for a cool new character!